The purpose of this study was to determine whether there was a difference in knowledge and application of the SIOP ® Model among in-service teachers who participated in an online professional development course on the SIOP® Model. Although these teachers all participated in the same course, information on the number of English Language Learners (ELLs) in their classrooms was used to distinguish teachers who received the training in a Just-in-Time (JiT) context, as opposed to those who received the training in a Just-in-Case (JiC) context. A secondary purpose of the study was to determine whether implementation of the Dick and Carey Systems Approach Model would result in a valid, quality online curriculum. The online curriculum on SIOP® was developed based on the guidelines for instructional design according to the Dick and Carey Systems Approach model, and the documentation created as part of the Dick and Carey model was reviewed and evaluated by instructional design or SIOP® content experts, as appropriate, at each step. Rubrics created for the purpose of assessing alignment with the Dick and Carey model were also evaluated by subject matter experts for construct and face validity. A Repeated Measures Analysis of Variance was used to analyze whether there was any statistically significant difference between learners who received JiT versus those who received JiC instruction. Results from the data analysis revealed no significant difference in knowledge or application skills between the JiT and JiC groups. However, there was an increase in learner application of SIOP® Model principles in classroom teaching, for both groups, as demonstrated by significant increase in scores on the Post-instruction Lesson Plans. Participants in the JiT group did not perform any better than the ones in the JiC. Therefore, JiT training did not emerge as a better training strategy than JiC training. The main benefit of the training delivered through this study seemed to be in increasing application and not knowledge. Results from the Focus Group Meetings indicated that timing of the course was unsuitable for implementation of SIOP® principles in actual classroom practice. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]