It’s or Its
The difference between its and it’s is easy to learn but can be hard to implement consistently. Even as an adult you sometimes have to pause and remind yourself that it’s is a contraction of it is and there is no possessive apostrophe in its (even if it feels like there should be).
Spell-check is generally good enough to catch any mistakes on a computer, but that sometimes makes it harder to get it correct when you hand write. Unfortunately, like many other easily confused words the only way to prevent mistakes is to practice.
While kids are learning it can also be helpful to have reminders posted around the classroom. This could be a fun, creative project to do.
Brainstorm other easily confused words as a class (seeing that their teacher and classmates sometimes get confused could also help students to become more comfortable with making mistakes). After coming up with a list of words, break into smaller groups to come up with tips to help with remembering. A top tip I provide my students when learning the words their and there, is making the i in their into a little person, allowing them to remember their means ‘something belonging to a person.’ This has always been a great memory tool. Another one for knowing the difference between the words, principal and principle is circling pal and telling students, your principal is your pal.
Have the students make fun and create posters to hang up around the classroom to help them remember the next time they struggle. Depending on time constraints, you could also add a presentation element where each group stands up and explains their words and how to make sure we never confuse them every again.