Left and Right Handedness
I'm afraid your science teacher is wrong. Handedness is a complex trait. It is not determined by a single gene, and can't be described as being dominant or recessive. Handedness does apparently have a genetic component, but many other factors are involved as well. See the Wikipedia article on handedness:


  Handedness displays a complex inheritance pattern. For example, if
  both parents of a child are left-handed, there is a 26% chance of that
  child being left-handed. A large study of twins from 25,732
  families by Medland et al. (2006) has indicated that the heritability
  of handedness is roughly 24%.
  
  To date, two theoretical single gene models have been proposed to
  explain the patterns of inheritance of handedness, the first by Marian
  Annett of the University of Leicester and the second by Professor
  Chris McManus of UCL.
  
  However, the growing weight of evidence from linkage and genome-wide
  association studies suggests that genetic variance in handedness
  cannot be explained by a single genetic
  locus. From these studies McManus et
  al. now conclude that handedness is polygenic and estimate that at
  least 40 loci contribute to determining this trait.


What may be confusing is that the preferred hand is often called the dominant hand, but that usage of the work 'dominant' is unconnected to the concept of dominance in genetics.