Supporting students with mathematics learning difficulties (MLD) as they transition from arithmetic to algebra remains a challenge within the special education and mathematics education research communities. This dissertation includes 3 manuscripts focused on how fifth graders with MLD develop algebraic understandings related to equivalence and functional thinking while participating in 20 small-group early algebra sessions. The first study examined how interpretations of the equal sign shift during an early algebra intervention. Further, this study investigated how using multiple representations supported the student's shift in understanding. The results of this study indicated that a fifth-grade student diagnosed with a mathematics disability transitioned from an operational interpretation of the equal sign to a relational-structural interpretation. The findings also indicated that a student could hold more than one interpretation of the equal sign at once and the problem context can encourage the use of one interpretation over the other. In the second manuscript, I argued that task design contributed to students' interpretation of the equal sign. Results indicated that using 2 sets of contrasting open number sentences encouraged students with MLD to reconsider their interpretation of the equal sign and pursue new strategies to complete the tasks. For the third study, I explored the shifts in functional thinking that a fifth grader with MLD named Keenan exhibited during a small-group early algebra instruction and how peer interactions contributed to this shift. Findings showed there were 2 critical interactions between peers that influenced the level of sophistication Keenan was able to generalize and represent functions. Taken together, these studies revealed that students with MLD can reason algebraically, and task design along with peer interactions can support shifts in algebraic reasoning. [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.]