Lack (of)
Indonesian students sometimes struggle because they lack of critical thinking skills.
It's true that lack collocates strongly with of, but only when lack is a noun. When lack is a verb, there is no of, as in the following example:
Indonesian students sometimes struggle because they lack critical thinking skills.
If you really want to use lack of then treat lack as a noun:
A lack of critical thinking skills sometimes causes Indonesian students to struggle.
Once again, in 'lack of', lack is a noun, not a verb!
Challenge!
With a friend, discuss the photo at the top of the page using lack and lack of.
Check out the song by GuruEAP - Lack of lack!