The conversion of AMPA-silent synapses into AMPA signaling ones is an often proposed expression mechanism for LTP. In the developing hippocampus AMPA-silent synapses do not exist in the absence of synaptic activation but are created by discrete synaptic activations at low frequency (AMPA silencing). In this study we have related the amount of LTP that can be obtained at different developmental stages to the amount of AMPA silencing that is observed at that stage. Using this approach we find that LTP during the second postnatal week is no more than a restoration, and stabilization, of the AMPA signaling that was lost by prior test frequency- induced AMPA silencing. This unsilencing of AMPA signaling was mimicked by application of the PKA- activator forskolin. Synapses that did not exhibit AMPA silencing (AMPA-stable synapses) did thus not exhibit LTP. As the relative degree of AMPA silencing decreases with development, after the first two postnatal weeks LTP manifests itself more and more as a "genuine" potentiation that goes beyond the naïve AMPA signaling strength. Our results suggest that the third and fourth postnatal weeks constitute a transition period during which LTP translates into its mature form from one that is explained by mere stabilization of the AMPA signaling state.