At all levels of government (i.e., federal, state and local), we spend $850B on education and $792B on the military, your guess of $1.2 trillion is not even close.

http://www.usgovernmentspending.com/year2009_US.html

Reducing class sizes from 25 to 15 would require 66% more teachers, lets guestimate that the cost of education would rise by 40% [1]. That's $340B for fairly small improvements in educational outcomes (0.04-0.12 standard deviations, according to stats posted elsewhere in this thread).

[1] Not all costs would scale upward with teacher salaries. We could sometimes repurpose 2 30 student classrooms into 4 15 student classrooms, and some administrative costs would scale with # of students.

I guess you've never heard of supplemental spending, black operations and whatnot. Defense spending isn't solely the defense department. We spend a great deal of money on intelligence services.

My response was solely to the quoted number of $70 billion or so. $80 billion is not a lot. It appears the number quoted was in 1984 dollars or something like that. Even then it still isn't a lot given that the defense budget then was around $300 billion.

I prefer spending money on education, health, peaceful purposes but not everyone agrees. The point I made though, still stands. It's a not a lot of money and it isn't as if we couldn't do it.

That's for the 1986 student population with 1986 dollars. If you correct it for the estimated 2018 student population and 2010 dollars, you're already around $190 billion. And that's not counting the cost of building new schools, or factoring in the rise in per-student spending. You're easily looking at well over a trillion dollars when all is said and done.

Also, decreasing the class size to 15 students wouldn't get you very much improvement over current class sizes. It's only for every incremental decrease below 15 that you start to see meaningful improvement.