To "think outside the box" is both a statement, skill, and idiom. As a statement and idiom, you would tell someone "Try and think outside the box with this problem." The meaning of the idiom is to think differently. unconventionally, or from a new perspective. You are instructing someone to think of unique solutions to a problem. Your sentence is slightly unnatural. You could finish it "Students lack the "think outside of the box" mindset" but what you may be trying to express is "Students lack the ability to think outside of the box"

think in an original or creative way. think about something, or how to do something, in a new, different or creative way.

Basically, it's a Skill; very good. It's the description of the Divergent (creative) reasoning.You may find it primarily in a "Design" environment. It refers to the ability to go "beyond the borders" => of the exterior appearence/ expectations/... to any kind of "assumption"/ prejudice, and create "the New" → the innovation. In words, it's simple... 2) Second: recently it also has become a "meme" (which is different from idiom): something that people say just because it goes around and sounds good. So if you meet someone who say "I think outside the box", or someone who asks you to "think outside the box" at work ... then they are boasting.

I never answered your question! "To think outside the box is a "catchphrase." Thinking outside the box is an "ability." A straightforward way of saying what you want to say is "My students lack the ability to think outside the box." Don't try to make it into a compound word. Since it requires boldness, or audacity, or courage to think outside the box, instead of saying "My students lack the ability to think outside the box," you might say "My students like the boldness to think outside the box," or "My students are too timid to think outside the box."

The correct phrase is "think outside the box." It refers to creativity. It is actually a reference to an old puzzle. The puzzle shows an square array of 3 x 3 dots, with plenty of space around the array. You are challenged to draw four straight lines, without lifting the pencil off the paper, that will go through all nine dots. The solution looks like this: https://tinyurl.com/ybfw2ohm To solve the puzzle, you have to use lines that go outside the 3x3 box. Many people fail because they assume that they are required to stay inside the box, although the puzzle doesn't say so. In order to solve the problem, you have to think about going outside the box--you have to "think outside the box." So it suggests not only creativity, but the ability not to let yourself be constrained by imaginary limits. A famous example of thinking outside the box involved the development of the car starter motor by Charles Kettering. Engineers had calculated that an electric motor powerful enough to start a car would be impractical--it would be too big, heavy, and expensive. Kettering realized that people were assuming a constraint that didn't exist. They were assuming that the motor had to deliver power continuously, for an indefinitely long period of time, without overheating and burning itself out. He realized that the car would start within a few seconds. The motor would need to run for a few seconds. It could be heavily "overloaded" safely, because it wouldn't have time to overheat. The "box" here was the idea that the motor had to be designed to run indefinitely. He realized that wasn't true. He "thought outside the box." Unfortunately, the phrase "thinking outside the box" became overused. It's an old, stale, management buzzword. It's now sort of a joke. In a situation comedy, to show that a boss is a fool, they may have him urge his people to "think outside the box."