I had Bs and a couple of Cs sophomore year with regular classes But now as an IB students I've got straight A. How would colleges react to that?
I think colleges would think that you studied harder and you are thriving. In your sophomore year, they might thought you were going through some problems because of your sudden increase in grades.
This depends on the specific college and whether or not they holistically review! If there were any extenuating circumstances sophomore year (for example, a loved one died or you had to work longer hours to support your family) you should definitely list them in your application. It's hard to say how colleges generally react, but, particularly if you touch on personal circumstances, they will most likely be impressed with your academic achievements and growth.
Hope this helps!
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