We regularly use musictheory.net to learn about and take quizes on scales, note durations, chords, and a variety of other fundamental music basics. The only drawback to the site is the lack of rhythm training.
That is why everyone needs to bookmark teoria.com.
There is a section of the site that trains your rhythmic dictation ability. That's when you hear a rhythm, then you have to write it out on a staff.
You can customize the training for specific note durations, so if you think that half notes and quarter notes are too easy, you can eventually add eighth notes, noted notes, and triplets. You can also do exercises in simple or compound meter.
I would go there right now to check it out and see where your level is - especially Grade 8 students, since we will have a quiz next class.