My parents once thought much the same of kindergarten and as such I never went to it, nor did any of my other siblings. Yet everyone accepts kindergarten as being helpful now.
Kindergarten, for me, was 1/2 a day - it was to introduce the idea of an organized school day to young children so when they started to attend full time, they would adjust easier. We had occasional activities with building blocks to learn how to count and did things involving letters and numbers to become familiar with them. Mainly, it was social, follow the rules, work together, listen to the teacher. (that was almost 30 years ago)
Today - Kindergartners learn how to:
Write their name.
Spell small words.
Add.
Read.
Use a computer...etc
They'll even do homework and take tests.
In fact - my kids were doing that in Pre-school (not Head Start, though. Even though it's all the same. We paid for ours, Head Start covers their cost)
Problems: Pre-school actually does boost children ahead, but soon after, education levels out and it doesn't necessarily ensure their quality of education will continue to be above. It's just becoming early kindergarten. . .and our daughter complained in K that she was just repeating everything she already knew, because a lot of students in K didn't go to Pre-school, so they're worlds apart, ability wise.
about 8 years ago, on a different forum, a K teacher complain that many students can't 'write their name, read their name, use scissors, recognize half of the letters in the alphabet, recognize all the colors and numbers' - and thus, they weren't ready for K, and, it just made teaching K that much more difficult.
a mother responded to her - shocked - saying 'I send my kid to K so you can teach her all of that, I didn't know I was expected to teach my kid those basics beforehand'
See - things have changed quite a lot.