Chinuch starts from infancy. One does not learn any real knowledge then, but one learns the appreciation of that knowledge and way of life.
We sent our son to the JCC for nursery and pre-K. It was basically like a public school with many who were not Jewish or religious. He was the only religious kid in his class there. He felt quite uncomfortable and out-of-place, and he did not do well. At 5 he had the personal and social development of a 3 year old. He was very insecure and mistrusting.
After 2 years in a real frum school, he is where he should be. B”H.