Support Secondary school students achieve broad mastery of the curriculum if they are taught with methods appropriate to their learning styles and they devote significant effort to their studies. █████ ██ ████ █████ ███████ ██ ███ ████████ ██ ███ ████████ ██ █ ██████████ █████████ ███████ █████ ████████ ███ ███ █████ ██████ ████ ███████ ███████████ ██ █████ ████████ ███████
The conclusion is that if broad mastery isn’t achieved, it must be that the students aren’t taught with appropriate methods. As support, the author gives a conditional premise: appropriate methods, combined with significant effort, lead to broad mastery. (Contrapositive: if broad mastery isn’t achieved, there either weren’t appropriate methods or there wasn’t significant effort.)
The premise says that a lack of broad mastery means one of two things: a lack of appropriate methods or a lack of significant effort. But the conclusion is that broad mastery means one thing only: a lack of appropriate methods.
The conclusion would follow if we assumed that when there’s a lack of significant effort, there must also be a lack of appropriate methods. In that case, no matter what, a lack of broad mastery always means a lack of appropriate methods.
The conclusion can be properly █████ ██ █████ ███ ██ ███ █████████ ██ ████████
As long as █████████ ██████ ████████ ███ ██████ ████ ███████ ███████████ ██ █████ ████████ ███████ ████ ████ ██████ ███████████ ██████ ██ █████ ████████
Contrapositive: if students don’t devote significant effort, it must be that they’re not taught with appropriate methods. This means that no matter what, a lack of broad mastery means that student’s aren’t being taught with appropriate methods.

Even if secondary ██████ ████████ ███ ██████ ████ ███████ ███████████ ██ █████ ████████ ███████ ████ ████ ███ ███████ █████ ███████ ██ ███ ██████████ ██ ████ ██ ███ ██████ ███████████ ██████ ██ █████ ████████
This says a lack of significant effort is sufficient for a lack of broad mastery. But this doesn’t change the argument’s core problem: a lack of broad mastery can mean either a lack of appropriate methods or a lack of significant effort. We’re still no closer to the conclusion.
Secondary school students ██ ███ ███████ █████ ███████ ██ ███ ██████████ ██ ████ ███ ███ ██████ ████ ███████ ███████████ ██ █████ ████████ ███████
This says a lack of appropriate methods is sufficient for a lack of broad mastery. But this doesn’t change the argument’s core problem: a lack of broad mastery can mean either a lack of appropriate methods or a lack of significant effort. We’re still no closer to the conclusion.
Teaching secondary school ████████ ████ ███████ ███████████ ██ █████ ████████ ██████ ████ ███ ██████ ██████ ██ █████ ███████ ██ ███ ██████████ ██ █████ █████████
This breaks the argument. If appropriate methods aren’t sufficient for broad mastery, then the author can’t possibly conclude that a lack of broad mastery always implies a lack of appropriate methods.
Secondary school students ███ ██████ ███████████ ██████ ██ █████ ███████ ██ ███ ██████ ███████ █████ ███████ ██ ███ ███████████
So significant effort isn’t sufficient on its own for broad mastery. This doesn’t affect the argument, which says significant effort is sufficient if combined with appropriate methods. It’s still possible a lack of broad mastery sometimes implies a lack of significant effort.