Cross-laminated-timber (CLT) panels, when used as shear walls or diaphragms are commonly connected with multiple fasteners in a row. For such connections, it is frequently observed that the load carrying capacity of multiple-fasteners is less than the sum of the individual fastener capacities. This phenomenon is referred to as “group-effect” which is accounted for differently in contemporary timber design standards for several types of fasteners. The research presented in this paper investigated the group-effect factor for self-tapping-screw (STS) shear connections between CLT panels. Different joint types (surface splines with STS in shear, and half-lap and butt joints with STS in either shear or withdrawal) were evaluated with a total of 122 quasi-static tests. The number of STS in one row was varied (1, 2, 8, 16, and 32) with their installation satisfying minimum spacing requirements. The results demonstrated that the effect of number of screws on joint capacity can be described using the expression neff = 0.9*n. For the reduction in stiffness, neff = n0.8 can be used.