Sam is studying how children respond to a new intervention for learning math and if it helps them later. She decides to follow two groups of children across several years of their life. What type of research design is this?
a)Cross-sectional
b)Longitudinal
c)Cross-sequential
d)double-blind

Longitudinal

Option B.

Explanation:

Longitudinal type of research design is a type of research design which takes in to consideration the same group for the study but this study goes on  for a long period of time.

This type of research design is longitudinal in the sense that the research has same group of students in it but the study will go on for many years to see the effect of the new method for learning math for different years of life of those students.