Britney Spears is taking lessons in pre-algebra so she can help her eldest son Preston, nine, do his school homework.
She said: "They go to a really hard school, and this week we had three hours of homework [a night].
"Some of it is hard for me. Next year when [Preston's] in fifth grade, he's going to be doing pre-algebra, and I'm taking classes so I know how to do it!"
The 33-year-old star - who also has eight-year-old Jayden with her ex-husband Kevin Federline - has revealed she operates a reward system at home for her two boys.
She shared: "If they get so many A's, they get one toy a month.
"Preston just asked for a high allowance like $10 a week or $20 a week - but we'll see."
Meanwhile, Britney - who has been dating producer Charlie Ebersol for six months - has admitted she would like to have more children "in the future".
She told PEOPLE magazine: "I would like to have one more. I am very satisfied with my two boys but maybe in the future."
When asked if she'd like to have a baby girl, she added: "I would love a mini-me. That would be fun!"