'deepened their understanding' is a perfectly correct and usable phrase in written English.
It can be used whenever you need to express that someone has reached a more thorough or complete grasp of a particular concept or idea. For example: The professor's lecture on physics deepened the students' understanding of the subject.
In recent years, scientists have deepened their understanding into the neural mechanisms behind this phenomenon.
But handling the objects deepened their understanding of how the mirrors, as well as all Chinese bronzes, evolved.
Drawn in to the colourful spectacle, dancers deepened their understanding of the history of the local community, while having the opportunity to demonstrate their place in it.
But in talks outside theaters across the country, nearly all of those interviewed said the film had delivered an emotional wallop and deepened their understanding of their faith.
The FC provided students with multiple resources, with representations and opportunities to engage with complex or abstract theory that improved and progressively deepened their understanding with each new representation, from video to seminar, and encouraged learning strategies that would lead to better learning outcomes (Jovanović et al., 2017).
As attitudes have opened up, medicine and psychology have deepened their understanding and resources have become more abundant.
"You have to deepen their understanding," she said.
They are using Islam to deepen their understanding of other traditions, and using other traditions to deepen their understanding of Islam.
The very enterprise was forcing them to deepen their understanding of the physical properties of the world...
Students become video editors and deepen their understanding of current climate change issues by producing a short film.
These "Beauty" performances showed Ballet Theater's artists deepening their understanding of what both this ballet and they themselves can be.
