Only if you make them. The trials are worth like 40-50%, so if you nail those and others don't go quite so well than you can easily jump up a few rankings.
YES THEY DO!
I was ranked =14th/27 in Biology at the end of term 4, after half yearlies I am now =3rd/26 (2nd bottom kid dropped
And both tasks were 20% weighting, so with the higher weightings of the next tasks ranks should be easier to change for both you and me.