**5. Conclusions**

This study demonstrates that children with Down syndrome can develop reading skills by 3rd grade. Our study extends the current literature by examining the age-specific occurrence of reading across the participants' first three years of school in Norway and by highlighting variables that may be underlying strengths of early readers with Down syndrome. Specifically, early readers exhibited significant strengths in vocabulary and letter knowledge skills prior to their reading onset, in addition to stronger nonverbal mental ability. As the children were pre-readers when these data were collected, the strengths cannot be attributed to learning via reading. Thus, these findings reinforce the need to consider children's language skills as well as their understanding of the alphabetical principle; early systematic training in vocabulary and play with letter knowledge could play a key role in promoting the development of early reading skills in children with Down syndrome.

**Author Contributions:** Conceptualization, K.-A.B.N. and E.S.; methodology, K.-A.B.N. and E.N.; formal analysis, E.N. and K.-A.B.N.; investigation, K.-A.B.N.; resources, K.-A.B.N.; data curation, K.-A.B.N.; writing—original draft preparation/introduction K.-A.B.N. and E.S./method K.-A.B.N. and E.N.; results E.N.; discussion K.-A.B.N. and E.S.; writing—review and editing, K.-A.B.N., E.S., and E.N.; visualization, K.-A.B.N. and E.N.; project administration, K.-A.B.N.; funding acquisition, K.-A.B.N. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Research Council of Norway, grant number 238030.

**Institutional Review Board Statement:** Regional Committee for Medical and Health Research Ethics Sør-øst. IRB ID: 19732.

**Informed Consent Statement:** Informed consent was obtained from all families involved in the study.

**Data Availability Statement:** The data are available in the services for sensitive data at the University of Oslo and can be obtained by contacting the first author.

**Acknowledgments:** We would like to thank the participating children and parents, schools and research assistants as well as the funder of the study: grant number 238030 from the Research Council of Norway.

**Conflicts of Interest:** The authors declare no conflict of interest.
