Concerns about academic dishonesty have long been a factor in teachers keeping tests. There is also a belief that giving the exact same test over time serves as a type of "standard" among grade levels.
Although students may not be allowed to bring their completed tests home, interested students may often take notes while teachers are reviewing the test, so they may learn from any problems they did not solve correctly. A student making an appointment to visit a teacher during office hours also shows keen interest in learning from one's mistakes.
Not saying that this is happening in your son's school, but some parents have shared what may be an emerging trend toward teachers/schools/districts testing/assessing student knowledge beyond that which has been taught in the classroom. While there is a place for such tests and assessments, many would agree that a "class grade" ought to be relative to mastery of material taught in that class. (By contrast, screening for some programs may consist of above-level items and an institution may not care to distinguish whether a student learned the material in school, self-driven study, summer math camps, enrichment courses, or through private tutoring.)
In some districts, teachers are held accountable for their students' mastery of the course material and therefore these teachers may work very diligently to scaffold support for students who may hit occasional sticking points. However if a student does not contact the teacher to request assistance, the student may be suggested to drop the course for one in which both student and teacher may experience greater success.
If the current schedule of Honors subjects is a bit overwhelming, DS may wish to consider his interest and affinity for any subject, as separate from his expertise or current performance in that subject. With parental guidance and feedback, he may wish to choose one or two subjects to study at the Honors level, and focus on those? He may wish to consider choosing whether to study other subjects at the regular grade level. The level of challenge/frustration which is most appropriate, while keeping one's life in balance, can often be best determined by the student. Coaching/feedback from a trusted source (often parents) can help. As a parent you may wish to think about Carol Dweck's "growth mindset" and speak to him about this in relation to his decision(s) about what level to study each subject at.
For example, if DS decides to continue with a number of challenging Honors-level courses and may earn a lower grade than he would have in the regular classes, is he prepared to promote the view that he developed "growth mindset" and rose to the challenge, working through the difficulties, rather than backing away and settling for the sure thing? High grades are one type of reward, while rising to a challenge and mastering something new is another type of reward.
The level of challenge at which DS feels his life is in balance will be the best (or least-worst) path for him at this time.
Don't know if the ideas in this post help, but they are meant to agree with what you observe about your son's classes and also say that good things can be found regardless of which path he takes (Honors courses, regular grade level courses, or a combination). Ultimately what matters most may be his sense of being empowered to make the choice(s) and follow through, while being supported by those who mean the most to him, his family.
