  The exceptional spectra of the most luminous $z>10$ sources observed so far
have challenged our understanding of early galaxy evolution, requiring a new
observational benchmark for meaningful interpretation. As such, we construct
spectroscopic templates representative of high-redshift, star-forming
populations, using 482 confirmed sources at $z=5.0-12.9$ with JWST/NIRSpec
prism observations, and report on their average properties. We find $z=5-11$
galaxies are dominated by blue UV continuum slopes ($\beta=-2.3$ to $-2.7$) and
inverse Balmer jumps, characteristic of dust-poor and young systems, with a
shift towards bluer slopes and younger ages with redshift. The evolution is
mirrored by ubiquitous CIII] detections across all redshifts (EW$_{0}=5-14$
\r{A}), which increase in strength towards early times. Rest-frame optical
lines reveal elevated ratios ($O32=7-31$, $R23=5-8$, and $Ne3O2=1-2$) and
subsolar metallicities (log O/H$=7.3-7.9$), typical of ionization conditions
and metallicities rarely observed in $z\sim0$ populations. Within our sample,
we identify 57 Ly$\alpha$-emitters which we stack and compare to a matched
sample of non-emitters. The former are characterized by more extreme ionizing
conditions with enhanced CIII], CIV, and HeII+[OIII] line emission, younger
stellar populations from inverse Balmer jumps, and a more pristine ISM seen
through bluer UV slopes and elevated rest-frame optical line ratios. The novel
comparison illustrates important intrinsic differences between the two
populations, with implications for Ly$\alpha$ visibility. The spectral
templates derived here represent a new observational benchmark with which to
interpret high-redshift sources, lifting our constraints on their global
properties to unprecedented heights and extending out to the earliest of cosmic
times.
