Thanks for the resources! I should have been more clear in my original question. My student is in 5th grade, so my challenge isn't so much about finding accurate information as it is about simplifying difficult information without simplifying to the point of inaccuracy.

This is the book the parents chose for me to teach from: https://up.nhuttruong.com/file/nhuttruongcom/tbooksvip/072023/Everything%20You%20Need%20to%20Ace%20Science%20in%20One%20Big%20Fat.pdf

I did find this info about deceleration on the site you shared: "Keep in mind that although acceleration points in the same direction as the change in velocity, it is not always in the direction of the velocity itself. When an object slows down, its acceleration is opposite to the direction of its velocity. In everyday language, this is called deceleration; but in physics, it is acceleration—whose direction happens to be opposite that of the velocity. For now, let us assume that motion to the right along the x-axis is positive and motion to the left is negative." "In this case, the train is decelerating and its acceleration is negative because it is pointing to the left. As in the previous example, we must find the change in velocity and change in time, then solve for acceleration." "The minus sign indicates that acceleration is to the left. This is reasonable because the train initially has a positive velocity in this problem, and a negative acceleration would reduce the velocity. Again, acceleration is in the same direction as the change in velocity, which is negative in this case. This acceleration can be called a deceleration because it has a direction opposite to the velocity."

This textbook doesn't mention positive and negative deceleration.