Student or Learner
The first two years have been successful.
The subject 'The first * years' always goes with a plural verb form. Does a singular form of verb work too?
The first two years has? been successful.
If you consider the two-year period as one unit, you can use "has."
If you consider the two years as individual units, you use "have."
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.