So it goes with our kids' school skills and mental abilities. If all goes well, our kids' brains should be constantly evolving, growing, and making new connections. If they aren't, we must notice and correct whatever is going wrong as soon as possible. Unlike not noticing your child's physical development, letting precious time slip by without noticing and/or acting on a lack of brain development can cause real harm. After all, the further a child falls behind, the harder it is to catch him or her back up.
To keep track of what your kids know and/or don't know, you need to constantly test them. Sometimes, this can be done informally by simply calling on your kids to answer a variety of relevant and telling questions while making a mental note of who knows what. Having your students complete written assignments on their own can also help give you a quick, informal peek at how they are progressing. Other times, however, you will need to test your kids more formally, calling them up one-on-one to answer a specific set of questions geared to expose any hidden weaknesses and/or problems that might exist.
Testing your kids is not just about finding out who is succeeding and who is failing; it's about uncovering any gaps or potential weaknesses and filling them in before they have a chance to cause a major problem.
Stay on top of your kids' mental progress. Take "photos" throughout the year by formally testing your kids every 6-9 weeks. This will give you a wonderful record of their growth that otherwise might go largely undetected. Pull these records out at each Parent/Teacher Conference, and marvel at the growth that has taken place. Use them to point out what you want to see fill in next as well. This will help everyone get a good peek at whatever growth has (or hasn't) taken place, just like an old picture one stumbles across from time to time!
All the best,