Your journal will help you chart his progress in ways that make sense to you. Take pictures or videos. Make a memory book. Create a portfolio or a wall that he can fill with all his favorite work. Look at it often and notice his progress.
True assessment compares progress between one point in time and another.
Finally, be an integral part of your child's learning life. Learn to listen carefully and to work and learn together with her. Be a model of active learning for her. Continue to be that careful observer and watch her as she works, because what worked last year or last month or even yesterday may not work tomorrow. Children grow and mature and their needs often change as that happens.