While many in the early Church were fully immersed in a river or lake as part of Chrisitan Baptism, the practice was not universal. In the Scriptures we read of those who were converted in great numbers, and there were those who were converted in prison and other places where they did not have access to large bodies of water, but we read they were baptized. Baptism as well as the Eucharist, Marriage, some of the ceremonies of Confirmation and the ordination to the priesthood are carried over from Judaism. How they differ is that Jesus elevated these ceremonies to be a rite which He uses to confir Grace upon us.
If your teacher (as most Evangelicals usually do) wishes to interpret the Bible for themselves as the only source of doctrine, then he or she will have to face up to the fact that Baptism was documented by the early Church Fathers as being valid be it by sprinkling, pouring or immersion. If they wanted to do it as Jesus (who’s baptism was not the same as ours, but rather the Baptism of John the Baptist, which the scriptures tell us could not save.) Then we would also only be able to accept baptisms that were not simply by full immersion, but also were in living water, which per Jewish law cannot have been transferred through a metal or clay pipe, but must be from a natural spring, or river. So any Evangelical baptism that takes place in a large baptisimal tank, or pool is not a valid baptism (using their Evangelical arguments that only what they interpret from the Bible is valid).
Most Evangelicals will disregard the writings of the Early Church Fathers, which while not equal to the Scriptures do tell us what the Apostles and Early Church believed and taught. If we read the Scriptures and the Fathers, the Faith taught and believed is found in the Catholic Church, and not in the abbreviated, and divergent doctrines of the Protestant Churches