often, oft in

Often or often ( one word ) means frequently, or on many occasions --
Is he often this grouchy?
It's our favorite restaurant; we go there often.

Oft in or oft in ( two words ) is an old-fashioned or poetic term meaning frequently ( oft ) [ followed by in ] --
"Oft, in the stilly night..."
The bard is oft in love; it fuels his poesy.

Now that you know that, you can say--
"The students were oft in high spirits, and even more often in trouble."