At each grade level expect more responsibility from your child. I must give kudos to my daughter. I only had one child and she was and is great. But as a former therapist I frequently taught parenting classes and helped families with many issues.
1) Expect responsibility. Allow them to handle the consequences if they forget something.
2) Teach them how to prepare. The night before help them get their things together. Show them you do the same thing ( helpful for you too).
3) Remind them once in the morning and ask them to remind you. This really makes it fun.
4) When they forget something and they will. Allow them to handle the consequences. Don't be angry. Talk about what they can do so it doesn't happen again.
5) Deflect excuses and share a time when you forgot something or if you would forget something for work, what the consequences were or/would be. Remember mistakes happen and if you nip it in the bud it won't become a pattern.
6) Use the same logic to incorporate these into the routine as the ages/grades change to make them age appropriate.
Hopefully they w develop a good pattern that will help them even in adulthood.
My daughter uses these techniques with my grandsons, 11 & 6. So far so good. :)
Good luck parents and hope this was helpful.
Anne Marie Brooks