The purposes of this study were two folds. First was to design three strategies to help elementary school children reading science expositories online with the supports of an annotation system. The "iRuns" strategies were proposed based on the SOI model of Reading expository text  to include (1)"underline" for selecting main ideas, (2)"annotation for connection" to organize important ideas and (3)"summary" for integrating multiple concepts. Then a field study was conducted to explore whether students efficiently adopted iRuns strategies and achieved comprehension on earth science materials. A total of 55 5th and 6th graders from an elementary school participated a 8-week reading club. A plug-in annotation system (COM2ANNO) developed by Huang et al.  was adopdeted. Students underlying, annotation and summary efficiencies were rated more favorable if they hit more main ideas. The results showed that iRuns strategy efficiencies decreased slightly across multiple time points and the high reading ability students' three annotation efficiencies were always better than the low ones. The gaps of iRun strategy efficiencies between high and low reading ability groups was gradually getting closer through series of instruction. Low ability students' strategy efficiencies correlated with comprehension score significantly but the high ones didn't. It indicated that low reading ability students benefited greatly from the iRuns strategies instruction. The annotation efficiecy was affected by using different types of annotating method (type vs. Copy-paste). Typing resulted in shorter annotations while copy-pasting produced better quality of annotation which demonstrated more highly relevant main ideas selected across texts.