Suitable for all ages. When you sign up for Vocabulary.com you will be given an assessment quiz in order to give you suggested lists with which to start your practice. After completing the assessment you can use the practice lists suggested by Vocabulary.com or choose your own lists from the huge gallery of vocabulary lists.
One of the aspects of the Vocabulary.com activities that I like is the instant feedback for every practice question you attempt. It also has an iPad app ($4.19).