Many students are familiar with the video game paradigm of achievement based on trial and error. A course could be designed in a way that allows students to complete different modules whenever they are able to. This structure allows students to explore and gain proficiency in branches they find most interesting. Different modules could be linked in sequence or as prerequisites to advance or unlock other modules.
Because it is achievement based, students are given the freedom to try and pass assessments as many times as needed without the time pressure of getting it or getting passed up by the rest of the class.
Because students move at their own pace, there is less down time wasted. High achievers can move faster. Slower students can repeat as many times as necessary. Students can control their own schedule and make choices about organizing their work time.
Minimum requirements could be set that are flexible so that students can pursue their own mix of topics, and these choices would then inform their future course selections.
Instead of grades, students would have an achievement transcript with proficiency scores in each module. Assessors would have detailed information that could be analyzed as to how quickly a student progressed and which areas are strengths and weaknesses.
An achievement based curriculum would integrate well with independent or home school programs and advances in internet based software would make such courses easy to implement and spread.