Greetings Jon,
I hope what I say doesn't discourage you. And please note that I'm very very picky when it comes to the GUI of a program.
First thing that hit me that looked out of place was the initial window where you create, open or exit. The exit icon is not of the same stock as the other two icons which made me wonder why there is this one nice icon and two older looking icons mixed in one place. Go with one style or the other, but try not to mix between icon styles.
When I get to the program, it was a bit overwhelming due to the amount of controls. Maybe that can't be helped and is not so overwhelming that the program can't be used.
The next problem I had was the color choices between the backgrounds and the text colors. I'd go with a brighter text color imho. Same with the push buttons.
The GUI over all has some inconsistencies, mainly in the group boxes. In one box there's a lot of space on the left and right, in another, not space to the left and right. In one box, no space at the top of it and some at the bottom, but in other boxes, no space at the bottom at all and some space at the top of the box.
But out of all that I noted, I feel that the text color is the one that would need the most attention. If your users have to sit there for a bit to scan the text of the labels in order to make them out, then they might get annoyed and not use the program. The rest of the stuff I noted isn't as big of a deal to me as the text color. Those text labels need to be as distinguishable as possible for the user.
Being that I've worked with some driving schools in the USA before, I'm already a bit familiar with a lot of the info needed in this situation and I must say that it looks like you've covered what's needed for this type of program.
If I were a driving instructor... Would I buy this program. Honestly, no, unless I was a good friend and wanted to support you as a friend. Why? Needs a much nicer interface. Would I buy this program if had a more professional looking interface? Yes!!! You got the idea down, but merely need to work on the gui some, and then you'll be there with an excellent program.
Again, do not take this hard or get discouraged. I'd rather be honest with you than be like some people where they are too afraid to say anything at all, or lie and say "Yes, looks excellent" or something like that. Though I don't always come across the right way and sound harsh. I'm not trying to be harsh, just helpful.
Browse the internet and see if there are any similar programs to yours, and if so, look at their interface and see what it looks like. Then maybe check out some programs of the same nature, but not specific to driving schools. The idea here is to get a look at what others are doing with their interfaces. See if you can find out which programs you are looking at successfully selling and which are not, and then see if the quality of the GUI is any indication of the program's success. If so, then study the design of the successful ones you found and see what ideas you can use in your program's interface.
I really think your interface is near what it should be though, that merely putting in some more time on adjusting it a bit to be more consistent would do wonders. That, and text color.. If not the text color, then a darker background to bring out the current color of the text.
If you have any other questions, feel free to ask them here on the forums. I know there's are some really gui people in the Rev community, so one of them is sure to offer some answers or advice if you need it.
~Garrett
Nice work Jon.