What can you drive with a school bus CDL in Pennsylvania?

There is no "school bus CDL". You either have a Class C or Class B CDL with a school bus endorsement. A Class C, you can drive any bus under 26,001 lbs. GVWR. If you get a hazmat endorsement, you can transport hazardous materials in any vehicle 26,000 lbs. GVWR or less.

If you have a Class B, technically, you can drive any single vehicle with a Gross Vehicle Weight Rating of more than 26,000 lbs, but you're not going to get hired to drive a Class 8 with an unsynchronized manual transmission without any experience.