lag behind in
lag behind in (something)
To be or become tardy or late in doing something. The bank started putting a lot of pressure on us when we began lagging behind in our mortgage payments. I know that she is an excellent reader and writer for her age, so I don't understand how Sally can be lagging behind in language arts.
lag behind in something
to fall behind in something. I am lagging behind in my car payments. She is lagging behind in her homework assignments.