In my experience, CTD has been better for garden variety gifted students, but the MCT curriculum for their Core Essentials language arts courses is truly challenging. Here is my input on one of these courses. I'd like to hear your comments and/or your own experiences with this or the other CTD courses that incorporate MCT's curriculum.
My DD12 just completed CTD's "The Power of Language: Grammar I" course. The curriculum is by MCT (Michael Clay Thompson), who, if you're not familiar with him, designed an incredible system of language arts curriculum for gifted students.
Would I recommend it to others? That depends. Here are my thoughts:
1. DD began to love it about halfway through the course
2. DD began to apply what she had learned in this course to her writing within a couple of weeks of the start of the course
3.
It was VERY intense. I think MCT meant for the text to be the basis for a semester-long course, but the CTD course was only 2 months long
4. I think MCT meant for the text to be taught through lots of Socratic discussions between teacher and student, but the CTD course allowed for only 3 short (but sweet) audio discussions between teacher and the students, who were grouped according to time zones. The students were expected to learn the material through reading the textbook, and the audio discussions were for questions.
5. MCT has a unique way of "diagramming" sentence grammar, which he calls "the 4-level analysis". It's great, but
very time-consuming to type it into a word document. I worry some students could get turned off by this aspect of the course. (CTD's system can't handle scanned handwritten documents.)
6. CTD's audio conference platform is very touchy. 2 of the audio conferences had such poor audio quality that they were not useful.
7. Don't be thrown by the information on the course's blackboard site, which is accessible after the first day of the session. It's sketchy, confusing, and contradictory, so the two students I was in contact with just ignored most of it (despite my repeated suggestions that they ask the teacher for clarification) and did great.
8. The first 4 weeks were MUCH more intense than the last 3 weeks.
Either make sure your dc has 3-4 hours to spend every three days for the first 2 weeks of the class OR start on the first few chapters before the start of the course.9. The teacher really knew the MCT curriculum, and obviously had a lot of experience teaching the course to gifted students of this same age. She also had great rapport with the students during the audio conferences.
10. This particular MCT text is normally for 9th grade gifted students, but it is offered only to grades 6-8.
11. We studied the corresponding MCT vocab textbook for a couple of months before starting this course. If we hadn't done that, there would have been too many unfamiliar words in the grammar textbook. But my dd is bilingual, therefore her English vocab is lower than it would otherwise be, so you can look up a list of the MCT "Word Within the Word I" vocab words to see if your dc already knows them.
12. There wasn't as much interaction with other students as I would have liked. Not sure if it was due to the very complicated discussion forum platform on their BlackBoard site, but the students just never got in to interacting with each other.
13. Luckily, I have an example of how the MCT textbook for this course teaches grammar, to help you understand a bit about what it means to be a grammar textbook for gifted students: Abraham Lincoln's
Gettysburg Address is printed in full, with different-colored highlighting for each of the 5 different verb tenses that he used. MCT shows how President Lincoln used each verb tense to not only convey meaning, but also for emotional impact. It is within this context that the names and functions of these 5 verb tenses are taught to the students.
Looking forward to your questions, comments and/or experiences in other MCT CTD courses! 
