Upanayana is a term which is much heard and much debated. Now Upanayana has become a religious practice, but it was no so earlier. Upanayana was probably suggestive of student-life, which was called Brahmacarya in another term. Later, another ritual started before upanayana, which was called Vidyārambha. Generally Vidyārambha started at the age of five. But scholars think that — later vyākaraṇa and other studies were incorporated into the curriculum, so the time of Upanayana got delayed. So, after vidyārambha,preliminary studies started. After some years , around the age of eight, the boy was sent to the Guru̍s house for learning Vedavidyā and Brahmavidyā, with a mark of Upanayana.

Nī means ̍to take̍, and ̍upa̍ means ̍near̍ . Now, who is to be taken, to whom? Ask the question to any scholar, whether a Vaidika, Aupaniṣadika or a Smārta, the answer would be– to take a student to the Guru, for the purpose of learning.    Now-a-days, ̍poite̍ is often associated with the imagery of hair-cutting, ear-piercing, and wearing nine-string thread, but it was not so in the Vedic age. First of all, ̍upanayana; had nothing to do with hair-cutting or ear-piercing, because such rituals were over within two or three years of annaprāśana. After Upanayana, it was rather customary to keep a beard a hair. The presence of the yajñasūtra which is so common now-a-days, came much later within Brāhmaṇya rituals.

So, Upamayana was so easy at that time. Dradually, the vidyā-saṃvāda of students and teachers started losing its significance, and the desire to gain establishment in society as a Brāhmaṇa became more important.

Previously, the Ācārya used to impose certain regulations, considering the student-life of the disciple. Collecting samidha everyday and keeping the Gārhapatya fire alight was one of the duties of the Brahmacārī. Along with this, the student had to practice wearing the skin of an antelope, or keeping a beard– so that no pleasure or comfort could be indulged in. The kind of food which could excite the body, was completely forbidden. In Śatapatha, it was said that– being a brahmacārī, never drink madhu–
na brahmacārī san madhu aśnīyāt.

Besides, it is not permissible to sleep on a fine bed or a high place, dance and frolic, roam about here and there, and spit away whatever remains of food–
nopariśāyī syānna gāyano na nartano na saraṇo na niṣṭhīved.

Again, it is not permissible to go and sit in the cremation place, in a reclined and depressed mood–
na śmaśānamātiṣṭhet.

Among the labours to undertake, there is also the practice of asking for alms, that is, the practice of collecting one̍sown food. However, there was no scarcity of food, because the affectionate mothers of the neighbouring houses were ready to give alms to the young brahmacārī(s). On the whole, it can be understood that discipline, hardwork, and asceticism– these three were associated with learning in ancient times.

In Veda, Brāhmaṇa and the Upaniṣadic texts, the significance of Upanayana used to lie in a boy̍s practice of Brahmacarya. Such was the significance of Brahmacarya, that in many cases, the term Upanayana had not been used in the Brāhmaṇa-texts. Rather, terms like Brahmacārī, Brahmacarya, carried the significance of Upanayana. Secondly, At the time of Pahābhārata and Purāṇa, Upanayana was so common that there was little need of mentioning this ritual time and again. This ritual has remained almost without mention by name in Mahābhārata. Only once, in Ādiparva, when Draupadī gave birth to the sons of the five Pāṇḍava(s), their jātakarma and other rituals were performed according to Smṛti, and when they grew up , their cūḍākaraṇa- upanayana and other rituals were also performed by Dhaumya, the famuly-priest of the Pāṇḍava(s).
jātakarmāṇyāmupūrvāt cūḍopanayāni ca
cakāra vidhivat dhaumyasteṣāṃ bharatasattama.

It is also clearly stated in Mahābhārata that the sons of Draupadī started the study of Veda(s) as part of their upanayana.

Elsewhere in Mahābhārata, the concept of Brahmacarya, has come repeatedly. And in Śāntiparva, there is a detailed description of what should be the duties of an upanīta brahmacārī. In the context of Caturāśrama, it is said that in the first part of life, brahmacarya is to be performed. Brahmacarya is such a grand and prestigious performance that Mahābhārata says, even the sages and hermits can win over all loka(s) and seek the path of ultimate desire.
brahmacaryena vai lokān jayantī paramarṣayaḥ
ātmanaśca tataḥ śreyāṅyanvicchanmanasātmani.

Speaking of the duties to be performed by a Brahmacārī, Mahābhārata says– there is no place for jealousy or envy in the heart of a brahmacārī — brahmacārī anasūyakaḥ. A brahmacārī will stay in the house of the Guru or the son of the guru. The brahmacārī disciple will sleep after the Ācārya-Guru, and he will rise before his Guru. If the Guru does not have his meal, the disciple will not have his meal, if he does not drink water, the disciple will not drink water. Before coming to the study, the disciple will ask the Guru to give him lessons–