Here are some phrases you might consider:
- Rock this test!
- Keep up your good efforts!
- Soar high on the test today! (I've used this one on balloon paper)
- I'm really proud of your hard work. Now show what you know!
- Hard work pays off--cash in on it!
- It's Day 3--Stay focused! You're almost to the end!
Another way to encourage your students to do well is to do something like this teacher did: