Flexibility of decentralized controllable loads face the challenge of a lack of prediction data and missing integration mechanisms in order to provide their flexibility to the grid. FfE developed a smart market platform with a special focus on integrating small flexible systems. Therefore, an aggregation mechanism was developed as described in this paper. Based on an introduction to the platform process and the requirements to an aggregated flexibility offer the derivation of available flexibility by determining statistical simultaneity factors is described. Further different pool formation and aggregation schemes are analyzed. Finally, a case study and critical review leads to the outlook.