Naturalistic second language (L2) acquisition (i.e., L2 acquisition without classroom instruction) does follow ordered developmental sequences. These L2 developmental sequences need not be completely identical to the respective first language (L1) sequences. The L2 sequences involve some utterances which on the surface match certain phenomena familiar from L1 developmental sequences. Other L2 structures have no surface parallel to L1 and seem to be based on prior L1 knowledge. Therefore, the view that there is one universal developmental sequence for the acquisition of a language irrespective of whether it is acquired as L1 or L2 is inaccurate. These developmental sequences differ according to the child's prior L1 knowledge. The major part of the data for this study derives from systematic longitudinal observations of children with German as L1 acquiring English as their L2, as well as children with English as L1 acquiring German as their L2. (Author/CFM)