Standardized tests have come under fire as of late anyway regarding what they actually prove. They aren't abysmal either and I'd love to see something showing that. If you'd like a little reading material, take a look at this.
http://nces.ed.gov/Pressrelease/reform/
While it shows the US students not performing as well at grade 12 as foreign students, the push for college education has really mitigated the importance of such a thing. The US is 4th in college enrollment per capita beind Canada, S. Korea and Australia. While we aren't #1, we are in the top 5 and because our population is many times larger, we have more students in college which is what is truly important.
The job prospects for students without college are not as good as those who have college.
http://www.mapsofworld.com/world-top-ten/world-top-ten-university-students-countries-map.html (college enrollment source)
I don't quite understand how a religious belief relates to academic performance. Perhaps you can show a study that shows such relation. I think what you'll find is that US students haven't gotten worse, its simply that other countries have developed and are finally providing competition. I'm not quite sure how atheism or humanism is leftist indoctrination. Maybe you could explain that one to me as well. I guess those dirty godless commies are coming back around.
Yes, lets look back at teens killing others...teens like the James brothers and Billy the Kid. Killing is nothing new and teens have been killing people for a long time. Claiming that good christian upbringing is responsible for the good kids is like claiming that evil rock and roll and video games are responsible for the bad ones. Lets try a little personal responsibility instead.
Kids can still be taught about god, its just that people have finally realized that god belongs in the home and in the church, not in schools. You are basing your argument on the idea that morals and religion are mutually exclusive when it just isn't so.
Our laws are built on rights and liberties, not religious dogma. All humans are equal and as such, have rights. You are free to excercise those rights provided you don't prevent someone else from doing the same thing. No god is required. No christian mythology needed.
If you can show me some evidence for heaven and hell and eternal damnation, I'll be happy to rethink my stance. Otherwise, you're just using fear to keep the kiddies in line.