Kate Moss is being strict while her sister studies for exams.

The supermodel has been helping Lottie prepare for her GCSE [General Certificate of Secondary Education] tests and she has been making sure her younger sibling is staying focused.

An insider told The Sun newspaper: ''Kate can't help with the maths and chemistry because she says she's rubbish at it, but she's given Lottie the ultimate exam advice and told her no boys and no sneaking out of the house until the tests are over.''

Kate is said to be keen for Lottie to focus on her ''education'' before thinking about following in her footsteps with a full-time modelling career - and she's been checking in on her every day to make sure she's staying on track.

The source added: ''She always told Lottie that education is crucial. Kate wants her to finish school and then decide how much modelling she wants to do.''

Lottie certainly seems to be taking her sister's advice, taking to Twitter and suggesting her focus is completely on her studies.

She tweeted: ''So uninterested in any boys atm.''