They lacked the consistent planning and resources of the SSPCK.
The post-1790 Highland missionary movement was conscious that the SSPCK was unable to respond to all the opportunities in the Highlands largely because of lack of personnel.
This was a strategy quite different from that of the SSPCK in the earlier eighteenth century.
The SSPCK laid the foundation of the movement, but later bodies modified the approach of the SSPCK, especially by promoting the mother tongue (Gaelic) for communication.
The SSPCK may be seen as a pioneer missionary body that contributed to foreign missionary endeavor, largely by involving itself first in the Highlands, and then indirectly in North America.