Bob Rutherford, the authority's principal psychologist, said interim results for more than 2,000 pupils show that children are making statistically significant progress in reading skills. "The more intervention they have received, the greater their achievements," Mr Rutherford says.
Baseline assessment confirms what is "intuitively known" by all early years staff - that there is a huge variation in emerging literacy skills on entry to primary 1.
"Pupils from schoos serving more socially and economically deprived areas had significantly lower language skills than others, while in terms of gender, boys entered school with poorer pre-reading skills than girls," Mr Rutherford says.
Baseline testing revealed that knowledge of letters was the biggest single predictor of reading success. Other factors in order of significance were concept of print, word-word matching, awareness of beginning and end sounds of words, auditory discrimination, and expressive language skills.
Renfrewshire hopes that further baseline testing will allow primary teachers to identify at a very early stage which children are in need of extra support.