Campaigners condemn the 'three-for-two' seating rule
They claim it is wrong that vehicles with seats for 50 people can legally carry more than 80 pupils.
Meanwhile, ministers at the Welsh Assembly are due to discuss what they can do to help later in the week.
The law currently states that there is nothing wrong with sitting three children on a seat designed for two on their journey to school.
Many parents and teachers disagree. Their concerns are being highlighted throughout this week by the school transport safety group Busk.
Founder of the group Pat Harris said: "If you have children fighting for a seat, they will become unruly and distract the driver - and 95% of all accidents are driver error.
"It has been like this for the last 50 years. But the situation has changed, children are a lot bigger than they used to be, there are more roads and a lot more traffic, so you are more likely to have an accident.
"It is all to do with money and children's safety doesn't come high enough in some local authorities priority list."
Bus drivers and companies can face prosecution if they overcrowd public vehicles - but the rules for transporting children are different.
Campaigners say the law needs to be changed to protect youngsters in the same way as all other passengers.
To mark the week, mock emergency evacuation drills will be held at schools across Wales to teach pupils what to do in the event of an accident.
Policy review
Meanwhile, in light of public concern expressed about school bus safety recently, assembly ministers will be working with local authorities to review school bus policies.
Welsh Education Minister Jane Davidson and Welsh Transport Minister Sue Essex will consider whether the assembly is able to do more to improve safety measures.
This latest drive follows an accident last week in which 18 children and three adults were taken to hospital in west Wales following a crash involving a school bus and a council lorry.
The bus was taking 50 pupils to secondary schools when the accident happened on the A475 between Llandysul and Horeb at around 0840BST on Tuesday.
Most of the injured pupils were aged between 11 and 15 and were from Ysgol Gyfun Emlyn in Newcastle Emlyn and Ysgol Dyffryn Teifi in Llandysul.
Dyfed-Powys Police has said that an investigation into the cause of that incident is under way.