Are they in arrears?
First, what does your support order say about college expenses? Are they ordered? Is the child now attending college? Nothing can be attached unless it is ordered, and it cannot be attached in anticipation of a future need.
What type of pension are you inquiring about? Company pension? Payor's IRA? 401K? Cash Balance Plan? Makes a difference, as a pension may not be "owned" by the payor, but, the income generated may be subject to garnishment.