How important is a high school transcript for a transfer student?

A lot of people tend to not care or pay as much attention in high school and then realize it later in life. A transcript is very important to transfer. If you are worried about them not accepting you because of your high school record, I wouldn't worry about it so much. Since you have already shown your knowledge, drive, and will-power at your current college, it shouldn't be a huge deal and I would be very surprised if you weren't accepted. You'll do fine. Learning how important school is later in life is very common.