Why don't Schools follow latest IUPAC for naming groups? In high school I am taught that Group 7 were halogens and Group 8 were noble gases, and Group 3 the boron group, Group 4 was carbon group, etc. Then when I looked up the groups, I found that noble gases were group 18, halogens were group 17, Group 7 was the manganese group, ...

The school said that their numbering is based on counting valence electrons, and the transition metal columns have no business in their lessons.

So schools don't use IUPAC conventions.

How standard is their group name scheme?
The reason for this is that in 1988 (actually more than a few years back), IUPAC changed their naming system for the groups. Originally the transition metals didn't have a group number and weren't counted as a group. However now it is changed so that the transition metals do have a group number. So number instead of carbon being in group 4, it is in group 14. However despite this being changed quite a few years ago, you will still see in several websites and schools like your and mine still following the old IUPAC conventions and say that carbon is in group 4 rather than 14.

The reason that they do this I suppose is that it avoids confusion in students who are just picking up chemistry as they can see there is a clear relationship between valence electrons and group number. However besides this, schools do follow IUPAC conventions. 



References:

Pure Appl. Chem. 1988, 60, 431–436, DOI: 10.1351/pac198860030431

(thanks @Loong)