My son is left-handed, has very messy handwriting and an awkward pencil grip that slows his writing hugely. I’ve tried to show him a more comfortable grip but find it difficult as I’m right-handed. I’ve also mentioned it to the teacher but it hasn’t made any difference.
Handwriting is certainly trickier for left-handers. They are often unable to see what they have just written so it is not unusual for them to develop an awkward grip and an uncomfortable posture, often tilting their paper to severe angles. It’s a hard habit to change.