I personally have never heard of school 'suspensions' interfering with college choice, but perhaps things have changed.
Dunno if college's can access all of a kid's records, but as for any criminal records, those can be sealed when the kid is 18, provided they have fulfilled the obligations of their sentence.
Think again. In our local school district, Zero Tolerance means a kid can be suspended and transferred to an alternative (loser) school for the rest of the semester for anything that violates the school drug & weapons policy. Obviously this affects a student's GPA, what courses are available for them to take, what semester or year they will graduate...so yes, it affects their college options.
Some parents will say "that makes sense...keep the schools safe." Except that a Bic lighter is considered a "weapon," as is any sort of blade, including the one on a nail clipper (just like at the airport). Drugs? Not just the obvious ones, but things like Tylenol, Midol or any sort of OTC medication.
Zero Tolerance is just one of the dumber examples of the miserable failure of the War on Drugs, better known as the War on Teens.
As for permanent records being expunged after age 18, it's not that simple. I seriously doubt any record can disappear forever, although some records can become more difficult to access. My kid had his juvenile court record expunged after he turned 18, but guess what? The thing he most wanted to make disappear still shows up on his DMV record, for all insurance companies to see. It will stay there for 4 years, just like a traffic ticket would. So what good was the expunging? BTW, the incident had nothing to do with driving. In my state, any juvenile criminal offense is automatically attached to a minor driver's DMV record, and it doesn't just go away when he/she turns 18 -- regardless of what the courts do or don't do with those juvenile records.