Literacy is an important aspect of heritage language skills, and this paper examines the reading skills in the heritage language among Norwegian-American adolescents in the early 1900s. The data for this study is a Norwegian reader (Nordahl Rolfsen) with a corresponding glossary. This glossary was compiled by Ole E. Rølvaag, a well-known professor of Norwegian at St. Olaf College. The assumption is that the words he included in the glossary were those he knew -- from long experience teaching -- could cause difficulties for the students' reading of their heritage language. Thus, this present study represents a systematic examination of the listed words, which indirectly provides an insight into the reading skills of the young readers.