The present invention is directed to a method of making a functionalized elastomer, comprising the step of polymerizing a conjugated diene monomer in the presence of a lanthanide-based coordination polymerization catalyst activated with a functionalized aluminum reagent of formula 1 where R is a linear or branched alkane group containing 1 to 8 carbon atoms, and R1 is phenylene, or a linear or branched alkane diyl group containing 2 to 10 carbon atoms, or a combination of one or more phenylene groups and one or more linear or branched alkane diyl groups containing 1 to 10 carbon atoms; Q is of formula 2 where R5, R6 and R7 are independently a linear or branched alkyl group containing 1 to 3 carbon atoms or a group of formula 3 where R3 and R4 are independently phenyl or a linear or branched alkyl group containing 1 to 10 carbon atoms, or R3 and R4 taken together with the nitrogen atom represent a nitrogen containing heterocyclic group containing from 4 to 12 carbon atoms; or R5, R6 and R7 taken together with the silicon atom represent a structure of formula 4 where R8 is C1 to C4 linear or branched alkanediyl and Z is N or a group of formula 5 wherein R13 is C1 to C8 alkyl.