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 Balarāma exactly 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.
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.
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.