If you insist on "do it yourself" when your teen needs a driving instructor, be prepared to do the job right. After all, safe driving is a life skill well worth learning properly from the beginning. Your teen trusts you, but are you really prepared to do a comprehensive job as a teacher?
I've written about Perpetuating Mediocrity after I stopped a speeding vehicle and found a mother supervising her daughter at the wheel. The mother complained that she was unable to get the daughter to follow the speed limit. Personally, I think that we have two people at fault here. Mother not being prepared to be a good supervisor and daughter not following the rules of the mother's advice.
So, how do you prepare to teach your teen? The Teen Driver Source is a web site created by the Children's Hospital of Philidelpia. The "I am a Parent/Guardian" section contains 7 pages of good advice along with references to other useful materials.
Here's my two cent's worth.
You don't expect your teen in high school to learn everything from the teacher there, without doing any homework; in fact, they're probably going to be assigned more homework, timewise, than they spend in class.
And if you're an average parent, you don't expect to assume responsibility for providing your teen's entire education, either, home-schooling them while home-working them.
Education is, necessarily, part professional instruction and part practice.
In the case of Driver Education, a good driving school will provide solid instruction in specific skills (commencing with Vehicle Control - Starts, Stops, Turns, Reversing) - to begin with, and these skills will then be honed by practicing the same with parents. Depending on the student, it may take only a couple of hours but in all likelihood it will take a lot longer to become proficient in this.
Note that so far, we're not dealing with busy intersections and multiple conflicts. It's way too early, and trying to suddenly start dealing with these will only confound the basic learning - of vehicle control - that is the goal at this point.
Once the fundamentals have been covered, then the student is ready to deal with having the complications piled on.
But in every case, none of the process is random, and there's a clear understanding of the professional instructor's role, and the parent's role.
Think in terms of 12 hours' professional instruction; balanced with 48 hours' practice with parents - that's called homework, and it's irreplaceable.
Jumping in the car with your teen, now and then, to get on their case when they make mistakes, is not driver education.