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Serrations in the stress-time curve for a bulk metallic glass composite with microscale crystalline precipitates were measured with exceptionally high temporal resolution and low noise. Similar measurements were made for a more brittle metallic glass that did not contain crystallites but that was also tested in uniaxial compression. Despite significant differences in the structure and stress-strain behavior, the statistics of the serrations for both materials follow a simple mean-field model that describes plastic deformation as arising from avalanches of slipping weak spots. The presence of the crystalline precipitates reduces the number of large slips relative to the number of small slips as recorded in the stress-time data, consistent with the model predictions. The results agree with mean-field predictions for a smaller weakening parameter for the composite than for the monolithic metallic glass; the weakening parameter accounts for the underlying microstructural differences between the two.