Psychologists tell us that children tend to act out when there is conflict, turmoil and disruption at home. Often this happens at school. Your child's performance and behavior there may become an issue at trial to determine custody.
Failing grades, aggressive behavior and absenteeism will likely lead the judge to order an independent evaluation of your child, your spouse and you, to assess what is actually gong on within the family. In addition, teachers and other school personnel may be subpoenaed as witnesses, since they are in a position to give unbiased opinions on the daily mental and emotional condition of your son or daughter.
Once the layers of this legal onion start to unpeel, it is difficult if not impossible to conceal negative information and ugly facts. This is why divorce is a time to be honest and straightforward about what has actually happened in your marriage and to your children.
Of course, tell your attorney first - you are protected by attorney-client privilege. Your lawyer can then advise the best defense or way to proceed. Attempts to hide the truth almost always backfire. Remember this: where the child thrives, custody survives.