It is customary, after being initiated in the Gāyatrī mantra, for one to live away from home for some time under the care of the ācārya, to be trained in spiritual life. During this period, one has to work under the spiritual master as an ordinary menial servant. There are many rules and regulations for a brahmacārī living under the care of an ācārya, and Kṛṣṇa and Balarāma strictly followed those regulative principles while living under the instruction of their spiritual master, Sāndīpani Muni, who was a resident of Avantīpura, in the northern Indian district of Ujjain. According to scriptural injunctions, a spiritual master should be respected and regarded on an equal level with the Supreme Personality of Godhead. Kṛṣṇa and Balarāmaexactly followed those principles with great devotion and underwent the regulations of brahmacarya. Thus They satisfied Their spiritual master, who instructed Them in Vedic knowledge. Being very satisfied, Sāndīpani Muni instructed Them in all the intricacies of Vedic wisdom and in supplementary literature such as the Upaniṣads. Because Kṛṣṇa and Balarāma happened to be kṣatriyas, They were specifically trained in military science, politics and ethics. Politics includes such departments of knowledge as how to make peace, how to fight, how to pacify, how to divide and rule and how to give shelter. All these items were fully explained and instructed to Kṛṣṇa and Balarāma.
(Krsna Book).

The ocean is the source of water in a river. The cloud is created by the evaporation of ocean water, and the same water is distributed as rain all over the surface of the earth and then returns to the ocean in rivers. So Kṛṣṇa and Balarāma, the Supreme Personality of Godhead, are the source of all knowledge, but because They were playing like ordinary human boys, They set the example so that everyone would receive knowledge from the right source. Thus They agreed to take knowledge from a spiritual master.
(Krsna Book).

After hearing only once from Their teacher, Kṛṣṇa and Balarāma learned all the arts and sciences. In sixty-four days and sixty-four nights, They learned all the necessary arts and sciences required in human society. During the daytime They took lessons on a subject from the teacher, and by nightfall They were expert in that department of knowledge.
(Krsna Book).

Kṛṣṇa and Balarāma learned the art of dressing hair in various styles and fixing a helmet in different positions on the head. They also learned how to set up a theatrical stage, how to decorate dramatic actors with clothes and with flower ornaments over the ear, and how to sprinkle sandalwood pulp and water to produce a nice fragrance. They also learned the art of performing magical feats. Within the magical field there is an art called bahu-rūpī, by which a person dresses himself in such a way that when he approaches a friend he cannot be recognized.
(Krsna Book).

Kṛṣṇa and Balarāma also learned how to make various syrups and beverages required at various times, having various tastes and intoxicating effects. They also learned different types of sewing and embroidery work, as well as how to manipulate thin threads for dancing puppets. This art includes how to string wires on musical instruments, such as the vīṇā, sitar, esarāja and tamboura, to produce melodious sounds. Then They learned how to make and solve riddles. They learned the art of how even a dull student can very quickly learn the alphabet and read books. Then They learned how to rehearse and act out a drama. They also studied the art of solving crossword puzzles, filling up the missing spaces and making complete words.
(Krsna Book).

They also learned how to draw and read pictographic literature. In some countries in the world, pictographic literature is still current. A story is represented by pictures; for instance, a man and house are pictured to represent a man going home. Kṛṣṇa and Balarāma also learned the art of architecture—how to construct residential buildings. They learned to recognize valuable jewels by studying their luster and colors. Then They learned the art of placing jewels in a gold and silver setting so that they look very beautiful. They also learned how to study soil to find minerals. This study of soil is now a greatly specialized science, but formerly it was common knowledge even for the ordinary man.
(Krsna Book).

Kṛṣṇa and Balarāma learned how to speak and understand the languages of various countries. Not only did They learn the languages of human beings; Kṛṣṇa could also speak even with animals and birds. Evidence of this is found in the Vaiṣṇava literature compiled by the Gosvāmīs. Then They learned how to make carriages and airplanes from flowers. It is said in the Rāmāyaṇa that after defeating Rāvaṇa, Rāmacandra was carried from Laṅkā to Bhārata-varṣa on a plane of flowers, called a puṣpa-ratha.
(Krsna Book).

Kṛṣṇa and Balarāma then learned the art of foretelling events by seeing signs. In a book called Khanara-vacana, the various types of signs and omens are described. If when one is going out one sees someone with a bucket full of water, that is a very good sign. But if one sees someone with an empty bucket, it is not a good sign. Similarly, if one sees a cow being milked alongside its calf, it is a good sign. The result of understanding these signs is that one can foretell events, and Kṛṣṇa and Balarāma learned the science. They also learned the art of composing mātṛkā. A mātṛkā is like a crossword box, with three numbers in each row. If one adds any three from any side, it will come to nine. The mātṛkās are of different kinds and for different purposes.
(Krsna Book).

Kṛṣṇa and Balarāma learned the art of cutting valuable stones such as diamonds, and They also learned the art of questioning and answering by immediately composing poetry within the mind. They learned the science of the action and reaction of physical combinations and permutations. They learned the art of a psychiatrist, who can understand the psychic movements of another person. They learned how to satisfy one's desires. Desires are very difficult to fulfill; but if one desires something which is unreasonable and can never be fulfilled, the desire can be subdued and satisfied, and that is an art. By this art one can also subdue sex impulses when they are aroused, as they are even in brahmacārī life. By this art one can make even an enemy one's friend or transfer the direct action of a physical element to other things.
(Krsna Book).

Lord Kṛṣṇa and Balarāma, the reservoir of all knowledge, exhibited Their perfect understanding of all the arts and sciences mentioned above. Then They offered to serve Their teacher by awarding him anything he desired. This offering by the student to the teacher or spiritual master is called guru-dakṣiṇā. It is essential that a student satisfy the teacher in return for any learning received, either material or spiritual. When Kṛṣṇa and Balarāma offered Their service in this way, the teacher, Sāndīpani Muni, thought it wise to ask Them for something extraordinary, something no common student could offer. He therefore consulted with his wife about what to ask from Them. He and his wife had already seen the extraordinary potencies of Kṛṣṇa and Balarāma and could understand that the two boys were the Supreme Personality of Godhead. They decided to ask for the return of their son, who had drowned in the ocean near the shore at Prabhāsa-kṣetra.
(Krsna Book).

When Kṛṣṇa and Balarāma heard from Their teacher about the death of his son, They immediately started for Prabhāsa-kṣetra on Their chariot. Reaching the beach, They asked the controlling deity of the ocean to return the son of Their teacher. The ocean deity immediately appeared before the Lord and offered Him all respectful obeisances with great humility.
(Krsna Book).

On hearing this, Kṛṣṇa dove deep into the water and caught hold of the demon Pañcajana. He killed him on the spot but could not find the son of His teacher within his belly. Therefore He took the demon's dead body (in the shape of a conchshell) and returned to His chariot on the beach of Prabhāsa-kṣetra. From there He started for Saṁyamanī, the residence of Yamarāja, the superintendent of death. Accompanied by His elder brother, Balarāma, who is also known as Halāyudha, Kṛṣṇa arrived there and blew on His conchshell.

(Krsna Book).

Hearing the vibration, Yamarāja appeared and received Śrī Kṛṣṇa with all respectful obeisances. Yamarāja could understand who Kṛṣṇa and Balarāma were, and therefore he immediately offered his humble service to the Lord. Kṛṣṇa had appeared on the surface of the earth like an ordinary human being, but actually Kṛṣṇa and Balarāma are the Supersoul living within the heart of every living entity. They are Viṣṇu Himself but were playing just like ordinary human boys. When Yamarāja offered his services to the Lord, Śrī Kṛṣṇa asked him to return His teacher's son, who had come to him as a result of his work. "Considering My ruling supreme," said Kṛṣṇa, "you should immediately return the son of My teacher."

(Krsna Book).

Yamarāja returned the boy to the Supreme Personality of Godhead, and Kṛṣṇa and Balarāma brought him to his father. The brothers asked if Their teacher had anything more to ask from Them, but he replied, “My dear sons, You have done enough for me. I am now completely satisfied. What further want can there be for a man who has disciples like You? My dear boys, You may now go home. These glorious acts of Yours will always be renowned all over the world.

(Krsna Book).

Being ordered by Their teacher, Kṛṣṇa and Balarāma immediately returned home on Their chariot. They traveled at great speed, like the wind, and made sounds like the crashing of clouds. All the residents of Mathurā, who had not seen Kṛṣṇa and Balarāma for a long time, were very much pleased to see Them again. They felt joyful, like a person who has regained his lost property.

(Krsna Book).