Evidence

Fractions- Look at the work of the Rational Number Project.  You can find a compilation of the work from the University of Minnesota, find lesson plans, download fraction manipulatives and read of the success the project has had in public schools. 

In the Multisensory Math Program at ASDEC we use a similar concept based approach.  Students create fraction concept cards for the student notebook.  They choose their manipulatives and assemble card stock graphic organizers which they keep for reference.  The illustrate key vocabulary and concepts and all operations.  Reaction from teachers using them has been extremely enthusiastic.  "The children love them." 

There is evidence to support using circular models first and then transitioning to other models.  Teachers need to solidify concepts before teaching children to simply "push numbers around."  So many teachers tell me that they wish they had been taught this way.  You do not need commercial manipulatives to teach fractions either.  You can print fraction circles on cardstock.  You can use simple construction paper squares.  Folded paper can come later after students fully comprehend the concepts and remember:  fract- is a Latin root that means to break into parts.  I suggest that students need to cut or break something to really understand the linkage. 

In addition, students need to comprehend that the "fractions of one" is a place value concept.  This should be fully understood before decimals are taught.  Students will benefit from using manipulatives to add, subtract and simply fractions and mixed numbers.  Then, students can move on to the abstract level of experience using only numbers.