What law did I break? How much will the ticket be? Drove thru a school parking lot at night.?

Had an odd thing happen tonight. I live near a school with a long drive around it. Technically the drive is part of the school. The road says "Private Drive" although each morning the parents use the road to bring their kids to school, so it isn't really private. We are in a county in Texas (outside the city limits).

The public road on the other side of the school does not connect to the road by our house. The only way to get from that road to our road is another road about 3 miles away.

So tonight we were driving home on the road on the other side of the school, and we drove thru the 'private drive' to get to our street. A sheriff was there and pulled us over an gave me a ticket. The violation he wrote was "Cut through private drive to make a turn". No idea what the fine will be... it is not listed as one of the 'normal' fine items.

Now, I can understand how this would have been a problem if the two roads connected, and I had the option to turn from one to the other. But they don't connect anywhere. The only way to get from one to the other is thru the school drive. And again... parents do this every morning and afternoon (it is about 2 blocks from our house). If I was cutting a corner (like thru a gas station) to avoid a light, I would understand that. But this is not the case.

So, does anyone know what law specifically I broke? Any clue what the fine will be? Will I be able to take defensive driving?

Thanks!