  This work presents the medium-resolution ($R \sim 1,500$) spectroscopic
follow-up of 522 low-metallicity star candidates from the Southern Photometric
Local Universe Survey (S-PLUS). The objects were selected from narrow-band
photometry, taking advantage of the metallicity-sensitive S-PLUS colors. The
follow-up observations were conducted with the Blanco and Gemini South
telescopes, using the COSMOS and GMOS spectrographs, respectively. The stellar
atmospheric parameters (T$_{\rm eff}$, log$g$, and [Fe/H]), as well as carbon
and $\alpha$-element abundances, were calculated for the program stars in order
to assess the efficacy of the color selection. Results show that
$92^{+2}_{-3}\%$ of the observed stars have [Fe/H]$\leq -1.0$, $83^{+3}_{-3}\%$
have [Fe/H]$\leq -2.0$, and $15^{+3}_{-3}\%$ have [Fe/H]$\leq -3.0$, including
two ultra metal-poor stars ([Fe/H]$\leq -4.0$). The 80th percentile for the
metallicity cumulative distribution function of the observed sample is [Fe/H]$=
-2.04$. The sample also includes 68 Carbon-Enhanced Metal-Poor (CEMP) stars.
Based on the calculated metallicities, further S-PLUS, color cuts are proposed,
which can increase the fractions of stars with [Fe/H]$\leq -1.0$ and $\leq
-2.0$ to $98\%$ and $88\%$, respectively. Such high success rates enable
targeted high-resolution spectroscopic follow-up efforts, as well as provide
selection criteria for fiber-fed multiplex spectroscopic surveys.

Solar and Stellar Astrophysics;Astrophysics of Galaxies