Expecting all children to have the same educational outcome is inappropriate. It kills creativity and carries no interest for the child.
When you are working with your children, you know what they know & what they don't, so there is no need to test them.
Grades are irrelevant, as they generally don't define the child's potential, but only tells how the child compares to other children of a similar age.
In order for each student to have more meaningful experiences, they need to be able to participate in learning experiences that mean something to them.
Once your child takes an interest in something, he will study it without being asked to. If he is given the opportunity to work on a project, he will work on it until he is satisfied. This could mean five minutes, five hours, five days, or maybe even five weeks. That's OK. He is learning and making the most of the opportunity.
Children like to do a good job. Our brains are self-congratulators. This means that we feel good when we do a good job. We need to be sure to allow our children to study and create until they are satisfied.
One way to encourage them to do their best is if they are given an opportunity to show off what they've done and to celebrate their accomplishments.
When my children were young we would hold a special evening from time to time for the kids to give reports just to our family. We would make it a celebration with activities and refreshments.
A friend of mine held an open house in their home at the end of each school year to show off the great stuff they did all year.
Children don't need large rewards or praise, but it is effective for them to know that you and others appreciate their work – all without comparing them to anybody else.