In this study, a multi-element aerofoil including NACA2415 aerofoil with NACA22 leading edge slat is experimentally and computationally investigated at a transitional Reynolds number of 2×105. In the experiment, the single-element aerofoil experiences a laminar separation bubble, and a maximum lift coefficient of 1.3 at a stall angle of attack of 12°. This flow has been numerically simulated by FLUENT, employing the recently developed, k-k L-ω and k-ω SST transition models. Both transition models are shown to accurately predict the location of the experimentally determined separation bubble. Experimental measurements illustrate that the leading-edge slat significantly delays the stall to an angle of attack of 20°, with a maximum lift coefficient of 1.9. The fluid dynamics governing this improvement is the elimination of the separation bubble by the injection of high momentum fluid through the slat over the main aerofoil - an efficient means of flow control. Numerical simulations using the k-kL-ω transition model are shown to accurately predict the lift curve, including stall, but not the complete elimination of the separation bubble. Conversely, the lift curve prediction using the k-ω SST transition model is less successful, but the separation bubble is shown to fully vanish in agreement with the experiment. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.